Add sequence number to undo steps

third_party/WebKit/Source/core/editing/commands/UndoStack.cpp

Index: third_party/WebKit/Source/core/editing/commands/UndoStack.cpp
diff --git a/third_party/WebKit/Source/core/editing/commands/UndoStack.cpp b/third_party/WebKit/Source/core/editing/commands/UndoStack.cpp
index 7f435982f87767a5c40c03c6590b17436a7cefc5..1d9b91d6e6d61689bbdf1809846a6178080aa123 100644
--- a/third_party/WebKit/Source/core/editing/commands/UndoStack.cpp
+++ b/third_party/WebKit/Source/core/editing/commands/UndoStack.cpp
@@ -45,10 +45,13 @@ UndoStack* UndoStack::create() {
 }
 
 void UndoStack::registerUndoStep(UndoStep* step) {
+  if (m_undoStack.size())
+    DCHECK_GE(step->sequenceNumber(), m_undoStack.back()->sequenceNumber());
   if (m_undoStack.size() == maximumUndoStackDepth)
     m_undoStack.removeFirst();  // drop oldest item off the far end
-  if (!m_inRedo)
+  if (!m_inRedo) {

[yosin_UTC9, 2017/02/20 06:17:50]

nit: No need to have braces.

[Xiaocheng, 2017/02/22 02:47:32]

Whoops. Done.

     m_redoStack.clear();
+  }
   m_undoStack.append(step);
 }